Structural Relaxation of a Side-Chain Type Liquid Crystalline Polymer Having Long Spacer Chain: Analysis of Enthalpy Relaxation with an Activation Energy Spectrum

The decrease in enthalpy was measured using differential scanning calorimeter during thermal ageing for poly (6-(4'-cyanobiphenyl-4-yloxy) undecylacrylate) at various ageing temperatures. The relaxation function, derived from the enthalpy data, was found to have a stretched exponential form. The relaxation time was evaluated and the dependence on the ageing temperature was explained using an Arrhenius-type equation. The apparent activation energy was around 300 kJ/mol, lower than the values reported for some conventional polymers. The relaxation function was plotted against the reduced ageing time. It was found that the averaged relaxation time is a reduced variable. The fraction of free volume and the thermal expansion coefficient of the glass transition were calculated from a WLF plot for the relaxation time. The relaxation was analysed on the basis of the activation energy spectrum model.